The M134 Minigun is a 7.62x51 mm NATO, six-barreled machine gun with a high rate of fire (2,000 to 6,000 rounds per minute). It features Gatling-style rotating barrels with an external power source, normally an electric motor. The "Mini" in the name is in comparison to designs that use a similar firing mechanism but larger shells, such as General Electric's earlier 20-millimeterM61 Vulcan, and "gun" for a caliber size smaller than that of a cannon, typically 20 mm and higher.

"Minigun" refers to a specific model of weapon that General Electric originally produced, but the term "minigun" has popularly come to refer to any externally powered Gatling gun of rifle caliber. The term is also used to refer to guns of similar rates of fire and configuration regardless of power source and caliber.

The ancestor to the modern minigun was made in the 1860s. Richard Jordan Gatling replaced the hand cranked mechanism of a rifle-caliber Gatling gun with an electric motor, a relatively new invention at the time. Even after Gatling slowed down the mechanism, the new electric-powered Gatling gun had a theoretical rate of fire of 3,000 rounds per minute, roughly three times the rate of a typical modern, single-barreled machine gun. Gatling's electric-powered design received U.S. Patent #502,185 on July 25, 1893.[1] Despite Gatling's improvements, the Gatling gun fell into disuse after cheaper, lighter-weight, recoil and gas operated machine guns were invented; Gatling himself went bankrupt for a period.[2]

During World War I, several German companies were working on externally powered guns for use in aircraft. Of those, the best-known today is perhaps the Fokker-Leimberger, an externally powered 12 barrel rotary gun using the 7.92x57mm Mauser round; it was claimed to be capable of firing over 7,000 rpm, but suffered from frequent cartridge-case ruptures[3] due to its "nutcracker", rotary split-breech design, which is fairly different from that of a Gatling.[4] None of these German guns went into production during the war, although a competing Siemens prototype (possibly using a different action) which was tried on the Western Front scored a victory in aerial combat.[3] The British also experimented with this type of split-breech during the 1950s, but they were also unsuccessful.[5]

In the 1960s, the United States Armed Forces began exploring modern variants of the electric-powered, rotating barrel Gatling-style weapons for use in the Vietnam War. American forces in the Vietnam War, which used helicopters as one of the primary means of transporting soldiers and equipment through the dense jungle, found that the thin-skinned helicopters were very vulnerable to small arms fire and rocket-propelled grenade (RPG) attacks when they slowed down to land. Although helicopters had mounted single-barrel machine guns, using them to repel attackers hidden in the dense jungle foliage often led to barrels overheating or cartridge jams.[citation needed]

A U.S. Air Force rotary-wing crewman fires a minigun during the Vietnam War.

In order to develop a weapon with a more reliable, higher rate of fire, General Electric designers scaled down the rotating-barrel 20 mm M61 Vulcan cannon for 7.62×51 mm NATO ammunition. The resulting weapon, designated M134 and known popularly as the Minigun, could fire up to 4,000 rounds per minute without overheating. The gun was originally specified to fire at 6,000 rpm, but this was later lowered to 4,000 rpm.

The U.S. government had procured some 10,000 miniguns during the Vietnam War. By 1975, production of spare parts had ceased with the Army in possession of a large inventory. By 1985, there were few spares left in the inventory. Units that received miniguns could not maintain them, so by the 1990s only Task Force 160 (later named the 160th Special Operations Aviation Regiment (Airborne) or 160th SOAR) and some Navy Special Boat Units kept them in regular use. Around 1995, the 160th SOAR began acquiring spare miniguns. Industry had a difficult time reproducing parts according to the original blueprints, so models that were being procured were mechanically unreliable and mixed with the inventory of working spares. This resulted in using a mixed batch of working and unreliable weapons. This fact was unknown to the 160th SOAR, and the use of miniguns that would not work shook the unit's confidence in the system. The 160th was on the verge of dropping the Minigun from its inventory entirely, which would essentially have ended its service life in the U.S. military.[6]

Around 1990, Dillon Aero acquired a large number of miniguns and spares from "a foreign user". The guns kept failing to shoot continuously, revealing that they were actually worn-out weapons. The company decided to fix the problems encountered, rather than simply putting the guns into storage. Fixing failure problems ended up improving the minigun's overall design.[6] Dillon's efforts to improve the minigun reached the 160th SOAR, and Dillon was invited to Fort Campbell, Kentucky to demonstrate its products. A delinker–used to separate cartridges from ammunition belts and feed them into the gun housing–; and other parts were tested on Campbell's ranges. The 160th SOAR liked the delinker's performance and began ordering them by 1997. This prompted Dillon to improve other design aspects, including the bolt, housing and barrel. Between 1997 and 2001, Dillon Aero was producing 25–30 products a year. In 2001, it was working on a new bolt design that increased performance and service life. By 2002 virtually every component of the minigun had been improved, so Dillon began producing complete weapons with improved components. The guns were purchased quickly by the 160th SOAR as its standardized weapon system. The gun then went through the Army's formal procurement system approval process and in 2003 the Dillon Aero minigun was certified and designated M134D.[6]

The core of the M134D was a steel housing and steel rotor. To focus on weight reduction, a titanium housing and rotor were introduced, creating the M134D-T. This reduced weight from 62 pounds (28 kg) to 41 pounds (19 kg). The gun housing had a 500,000 round lifespan before it wore out, which was higher than a conventional machine gun's 40,000 round lifespan but was a reduced time for a rotary gun. A hybrid of the two weapons resulted in the M134D-H, which had a steel housing and titanium rotor. It was cheaper with the steel component, was only one pound (450 grams) heavier than the M134D-T, and had an increased lifespan of 1 million rounds.[7] The M134D-H is currently in use on various 160th Regiment platforms.[6]

Dillon also created specialized mounts and ammunition-handling systems. Initially, mounts were only made for aviation systems. Then from 2003 to 2005, the Navy began mounting Dillon miniguns on specialized small boats. In 2005, the Naval Surface Warfare Center Crane Division procured guns to mount on Humvees. In Iraq, US Army Special Forces units on the ground were frequently engaged by opposition forces, so they mounted M134D miniguns on their vehicles for additional firepower. After several engagements the attackers seemed to avoid vehicles with miniguns. Later the Special Forces units began concealing their weapons so opposition troops would not know which weapon they were facing.[6]

Garwood Industries created the M134G version with several upgrades to the original GE system. After extensive research, they determined that the Minigun's highest rate of fire may not be the optimum rate of fire for hit potential. After several extended firing exercises, Garwood concluded that the optimum rate of fire for the Minigun system is approximately 3,200 rounds per minute (rpm). This rate provides the operator with the maximum amount of target saturation while expending a minimum amount of ammunition. The M134G is being produced and offered with this firing rate as well as 4,000 rpm and the previous standard 3,000 rpm rate.[8]

Garwood Industries has implemented several other upgrades and improvements from the 1960s Minigun. The M134G system is being manufactured to military requirements such that all its components adhere to ISO standards to ensure quality traceability.[8] The upgrades include the following:

Drive Motor – Many positive improvements to the tried and true General Electric drive motor have been implemented using products not previously available. The new motor is lighter and also has an extended service life. Three proactive upgrades have been completed and the solenoid has been revised several times.[9]

Gun Control Unit – Garwood has upgraded the gun control unit using state-of-the-art electronics to guarantee unsurpassed reliability. A manual override for the booster assembly is standard on all M134G models.[10]

Feeder/Delinker – The Garwood feeder/delinker has an upgraded cartridge handoff system and has been finished with a new high-performance coating that will increase longevity and enhance operation in all environments.[11]

Barrel Clutch Assembly – The barrel clutch assembly has been re-engineered to both lighten the weapon system and improve performance. The newly designed flash suppressor completely eliminates the blinding flash that was a constant problem with older Minigun versions. New designs are being tested to even inhibit the sparks that are created from unburned powder and it is expected to completely eliminate the visual signature under fire.[citation needed]

Bolts – A new government model is being finalized that utilizes a new proprietary bolt design. The material and coatings used in this latest system greatly improve the longevity of the system and exceed current specifications.[12]

Grip Assembly – The M134G spade grip assembly is integral with the receiver through a new proprietary mounting lug. Previous versions only mounted to the clutch or other components. The new mounting area greatly improves the rigidity of the system.[13]

Rail System – The M134G incorporates a rail system that allows the easy mounting of several accessories that may be found useful to its operator. These include, but are not limited to, scopes, electronic sights, lasers and spot lights.[8]

The basic minigun is a six-barrel, air-cooled, and electrically driven rotary machine gun. The electric drive rotates the weapon within its housing, with a rotating firing pin assembly and rotary chamber.[14] The minigun's multi-barrel design helps prevent overheating, but also serves other functions. Multiple barrels allow for a greater capacity for a high firing rate, since the serial process of firing/extraction/loading is taking place in all barrels simultaneously. Thus, as one barrel fires, two others are in different stages of shell extraction and another three are being loaded. The minigun is composed of multiple closed-bolt rifle barrels arranged in a circular housing. The barrels are rotated by an external power source, usually electric, pneumatic, or hydraulic. Other rotating-barrel cannons are powered by the gas pressure or recoil energy of fired cartridges. A gas-operated variant, designated XM133, was also developed.[15] It is near identical but has barrels with ports that align with the piston drive in the center of the barrel cluster. It fired over 3000 rpm but was not put into production.[citation needed]

While the weapon can feed from linked ammunition, it requires a delinking feeder to strip the links as the rounds are introduced to the chambers. The original feeder unit was designated MAU-56/A, but has since been replaced by an improved MAU-201/A unit.[16]

The General Electric minigun is in use in several branches of the U.S. military, under a number of designations. The basic fixed armament version was given the designation M134 by the United States Army, while the same weapon was designated GAU-2/A (on a fixed mount) and GAU-17/A (flexible mount) by the United States Air Force (USAF) and United States Navy (USN). The USAF minigun variant has three versions, while the US Army weapon appears to have incorporated several improvements without a change in designation. The M134D is an improved version of the M134 designed and manufactured by Dillon Aero,[17] while Garwood Industries manufactures the M134G variant.[18] Available sources show a relation between both M134 and GAU-2/A and M134 and GAU-2B/A.[19][20] A separate variant, designated XM196, with an added ejection sprocket was developed specifically for the XM53 Armament Subsystem on the Lockheed AH-56 Cheyenne helicopter.[21]

Another variant was developed by the USAF specifically for flexible installations, beginning primarily with the Bell UH-1N Twin Huey helicopter, as the GAU-17/A. Produced by General Dynamics, this version has a slotted flash hider. The primary end users of the GAU-17/A have been the USN and the United States Marine Corps (USMC), which mount the gun as defensive armament on a number of helicopters and surface ships. GAU-17/As from helicopters were rushed into service for ships on pintle mountings taken from Mk16 20 mm guns for anti-swarm protection in the Gulf ahead of the 2003 Iraq War - 59 systems were installed in 30 days.[22] The GAU-17/A is designated Mk 44 in the machine gun series[22] and is generally known as the Mk 44 when installed on British warships.

The weapon is part of both the A/A49E-11 armament system on the UH-1N; and of the A/A49E-13 armament subsystem on the USAF Sikorsky HH-60H Pave Hawk helicopter. The weapons on these systems feature a selectable fire rate of either 2,000 or 4,000 rpm. There is mention of a possible GAUSE-17 designation (GAU-Shipboard Equipment-17), in reference to the system when mounted on surface ships, though this would not follow the official ASETDS designation system's format.[23][24]

One of the first applications of the weapon was in aircraft armament pods. These gun pods were used by a wide variety of fixed and rotary wing aircraft mainly during the Vietnam War, remaining in inventory for a period afterward. The standard pod, designated SUU-11/A by the Air Force and M18 by the U.S. Army, was a relatively simple unit, completely self-contained, with a 1,500 round magazine directly feeding delinked ammunition into the weapon. This means the Minigun fitted to the pod does not require the standard MAU-56/A delinking feeder unit.[25] A number of variations of this pod exist.

Initially on fixed-wing gunships such as the Douglas AC-47 Spooky and Fairchild AC-119, the side-firing armament was fitted by combining SUU-11/A aircraft pods, often with their aerodynamic front fairings removed, with a locally fabricated mount. These pods were essentially unmodified, required no external power, and were linked to the aircraft's fire controls. The need for those pods for other missions led to the development and fielding of a purpose built "Minigun module" for gunship use, designated the MXU-470/A. These units first arrived in January 1967 with features such as an improved 2,000 round drum and electric feeder allowing simplified reloading in flight. The initial units were unreliable and were withdrawn almost immediately.[26] By the end of the year, however, the difficulties had been worked out and the units were again being fitted to AC-47s, AC-119s, AC-130s, and even being proposed for lighter aircraft such as the Cessna O-2 Skymaster.[27] A fit of two MXU-470/As was also tested on the Fairchild AU-23A Peacemaker, though the Royal Thai Air Force later elected to use another configuration with the M197 20 mm cannon.[28]

In September 2013, Dillon Aero released the DGP2300 gun pod for the M134D-H. It contains 3,000 rounds, enough ammunition to fire the minigun for a full minute. The system is entirely self-contained, so it can be mounted on any aircraft that can handle the weight, rotational torque, and recoil force (190 lb (86 kg)) of the gun. The pod has its own battery which can be wired into the aircraft's electrical system to maintain a charge.[29]

Various iterations of the minigun have also been used in a number of armament subsystems for helicopters, with most of these subsystems being created by the United States. The first systems utilized the weapon in a forward firing role for a variety of helicopters, some of the most prominent examples being the M21 armament subsystem for the Bell UH-1 Iroquois and the M27 for the Hughes OH-6 Cayuse. It also formed the primary turret-mounted armament for a number of members of the Bell AH-1 Cobra family. The weapon was also used as a pintle-mounted door gun on a wide variety of transport helicopters, a role it continues to serve in today.